Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
  • C07C209/44—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of carboxylic acids or esters thereof in presence of ammonia or amines, or by reduction of nitriles, carboxylic acid amides, imines or imino-ethers
  • C07C209/50—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of carboxylic acids or esters thereof in presence of ammonia or amines, or by reduction of nitriles, carboxylic acid amides, imines or imino-ethers by reduction of carboxylic acid amides
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D201/00—Preparation, separation, purification or stabilisation of unsubstituted lactams
  • C07D201/02—Preparation of lactams
  • C07D201/12—Preparation of lactams by depolymerising polyamides
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
  • C08J11/16—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with inorganic material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2377/00—Characterised by the use of polyamides obtained by reactions forming a carboxylic amide link in the main chain; Derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L77/00—Compositions of polyamides obtained by reactions forming a carboxylic amide link in the main chain; Compositions of derivatives of such polymers

Definitions

• the invention relates to a process for the depolymerization of one or more polyamides into monomeric components in the presence of water by means of at least one alkali metal compound, at least one alkaline-earth metal compound or a mixture thereof.
• polyamides production waste for instance
• polyamide fiber spinners The reprocessing of polyamides (production waste for instance) has taken place for about 40 years, and is carried out in particular at polyamide producers and polyamide fiber spinners.
• this product reprocessing still takes place by means of the so-called phosphoric acid route.
• the drawback of this route is, however, that phosphate-containing production waste is formed, which in turn must either be worked up or be disposed of as waste.
• polyamides are relevant for the reprocessing, for example, fibers, films, chips and, injection molded or extruded polyamide products.
• the commercial feasibility of reprocessing polyamide-containing waste is directly dependent on the economic/technical possibility of converting the polyamide component of this waste into monomeric components which can, preferably, without further conversion reactions, be reused.
• the monomeric components are caprolactam and caprolactam precursors.
• Precursors are understood to be those compounds which can be used for the preparation of the polyamides without first having to be converted into caprolactam.
• An example of a precursor is amino caproic acid.
• the monomeric components are hexamethylene diamine and adipic acid.
• polyamides which can be depolynurized according to the invention are nylon-6, nylon-6,6, nylon-4,6, nylon-12, nylon-4,12, nylon-6,12, nylon-8, etc.
• polyamides are understood to be both polymers and oligomers of amides.
• Oligomers are understood to be both linear and cyclic oligomers of, for instance but not limited to, caprolactam.
• They are also understood to be polyamide-containing mixtures.
• the mixtures may also include compounds such as, for instance, colorants, UV stabilizers, matting agents, antistatic agents, impact modifiers, heat stabilizers, dirt-repelling additives, spinfinish oil, and other additives.
• This object is achieved by the depolymerization of one or more polyamides in the presence of water by means of at least one alkali metal compound, at least one alkaline-earth metal compound or a combination of an alkali metal compound and an alkaline earth metal compound at a pressure of between about 0.2 and about 2.0 MPa.
• Depolymerization preferably takes place at a pressure of between 0.5 and 1.8 MPa.
• the process of the invention relates to depolymerization of one or more polyamides into its monomeric components in the presence of water by means of at least one alkali metal compound, at least one alkaline-earth metal compound or a combination of an alkali metal compound and an alkaline earth metal compound.
• the depolymerization is conducted at a pressure of between about 0.2 to about 2.0 MPa.
• Suitable alkali metal compounds or alkaline-earth metal compounds are alkali metal oxides or alkaline-earth metal oxides, alkali metal hydroxides or alkaline-earth metal hydroxides, alkali metal carbonates or alkaline-earth metal carbonates and the alkali metal salts or alkaline-earth metal salts of amino caproic acid or the metal salts of linear dimer or trimer of amino caproic acid, rare-earth alkali metal hydroxides, rare-earth alkali metal carbonates or mixtures of these compounds.
• Examples of such compounds are sodium oxide, potassium oxide, magnesium oxide, calcium oxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, magnesium carbonate, sodium amino caproate, the sodium salt of the linear dimer or trimer of amino caproic acid, potassium amino caproate, the potassium salt of the linear dimer or trimer of amino caproic acid or a mixture thereof.
• sodium hydroxide and/or sodium amino caproate is used.
• the amount of alkali metal compound(s) and/or alkaline-earth metal compound(s) is generally at least 0.1 wt. % relative to the amount of polyamide to be depolymerized. Preferably, at least 0.2 wt. % of alkali (alkaline-earth) metal compound is used. In general, the amount of alkali and/or alkaline-earth metal compound(s) used does not exceed 2 wt. % of the alkali and/or alkaline-earth metal compound(s) used.
• the depolymerization is carried out by passing steam through the polyamide.
• the steam has a temperature of between about 220° C. and about 450° C.
• the temperature of the steam is between about 250° C. and about 350° C.
• the amount by weight of steam per hour is less than or equal to 3.5 times the amount by weight of polyamide.
• the amount of steam per hour is less than or equal to 2.5 times the amount by weight of polyamide. More preferably, the amount by weight of steam is the same as the amount by weight of polyamide.
• the reaction temperature i.e. the temperature of the molten polyamide, at which the process for the depolymerization according to the present invention is carried out, is between about 200° C. and about 400° C.
• the temperature is between about 250° C. and about 350° C., and more preferably the temperature is between about 250° C. and about 300° C.
• the polyamide Before the polyamide is contacted with the superheated steam, the polyamide is preferably molten. Melting preferably takes place in the absence of air (oxygen). The molten polyamide is depolymerized into its monomeric components. These monomeric components are discharged via a gas phase. In practice, the gas phase is then condensed to a condensate. It is possible to purify the condensate by hydrogenation or by a potassium permanganate treatment. The drawback of purification by means of a potassium permanganate treatment is that pyrolusite is formed. Preferably, therefore, use is made of hydrogenation, as described in U.S. Pat. No.
• This condensate may also contain linear and cyclic oligomers. These oligomers can be separated from the monomeric components, for instance by means of distillation as customarily employed by methods well known to those of ordinary skill in the art. The residue, including among other things, the alkali metal compound(s) and/or alkaline-earth metal compound(s), that remains after the distillation of the monomeric components, can be recycled to the depolymerization reactor.
• the process according to the present invention is eminently suitable for the processing of polyamide-containing waste; preferably, the waste is, if necessary, first mechanically reduced in size by, for instance, milling, chopping, tearing and/or cutting.
• Depolymerization according to the invention can be effected batchwise, semi-continuously or continuously.
• Example I From Table I it is evident that the conversion is significantly lower when the starting material was cyclic oligomers as compared to nylon-6 chips. Although a good conversion to caprolactam is achieved with H 3 PO 4 , the drawback was that 14 g of phosphate waste remained behind after the depolymerization. In contrast, Example I, according to the invention, produces no phosphate waste and produces a higher rate of conversion to caprolactam.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)
• Polyamides (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Citations (14)

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• 1997
  • 1997-05-01 NL NL1005942A patent/NL1005942C2/nl not_active IP Right Cessation
• 1998
  • 1998-04-10 TW TW087105474A patent/TW438771B/zh not_active IP Right Cessation
  • 1998-04-24 EP EP98201348A patent/EP0875504A1/en not_active Withdrawn
  • 1998-04-27 ID IDP980625A patent/ID20886A/id unknown
  • 1998-04-28 CZ CZ981310A patent/CZ131098A3/cs unknown
  • 1998-04-28 SG SG1998000885A patent/SG71785A1/en unknown
  • 1998-04-29 CA CA002236116A patent/CA2236116A1/en not_active Abandoned
  • 1998-04-29 BR BR9801507-9A patent/BR9801507A/pt not_active IP Right Cessation
  • 1998-04-29 KR KR1019980015247A patent/KR19980086657A/ko not_active Application Discontinuation
  • 1998-04-29 US US09/069,204 patent/US6087494A/en not_active Expired - Fee Related
  • 1998-04-30 PL PL98326098A patent/PL326098A1/xx unknown
  • 1998-04-30 JP JP10156543A patent/JPH111471A/ja active Pending
  • 1998-05-01 TR TR1998/00771A patent/TR199800771A2/xx unknown

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